<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script>
			var a=1;
			var b;
			
			console.log(typeof(a));
			console.log(typeof(b));
			
			console.log(a+b);
			
			b="b";
			console.log(a+b);
			console.log("--------判断是否是null--------");
			console.log(isNaN(3));
			console.log(isNaN('a'));
			
			var a1=NaN;
			var a2=NaN;
			console.log(a==b);
			//结果是false，在内存里false是0,0不是非数字
			console.log(isNaN(a==b));
		</script>
	</body>
</html>
